1. Field of the Invention
The present invention relates to a method for growing a Zn.sub.1-Y Mg.sub.Y S.sub.Z Se.sub.1-Z (hereinafter, referred to as ZnMgSSe) single-crystalline thin film, a ZnS.sub.X Se.sub.1-X (hereinafter, referred to as ZnSSe) single-crystalline thin film and a Zn.sub.1-W Cd.sub.W Se (hereinafter, referred to as ZnCdSe) single-crystalline thin film, and a method for manufacturing a semiconductor device by using the above growth method.
2. Description of the Related Art
ZnMgSSe, ZnSSe and ZnCdSe have been drawing attention as materials for a group II-V semiconductor laser which emits blue-green light. A single-crystalline semiconductor thin film made of these materials is formed by the molecular beam epitaxy (hereinafter, referred to as MBE) method. FIG. 1 shows a schematic construction of an MBE apparatus. Metals Zn, Cd, Mg, Se and Te, compounds ZnS and ZnCl.sub.2, and N.sub.2 gas are used for crystal growth in the MBE apparatus.
In growing ZnMgSSe single-crystalline thin film by the MBE method in The prior art, four independent effusion cells are each first filled with one of the four materials, elemental Zn, Mg, Se and polycrystalline ZnS (or elemental S) and then four kinds of molecular beams simultaneously irradiate upon the substrate from the effusion cells. The MBE apparatus is equipped with a pumping system, a substrate heating system, a plurality of effusion cells and a plasma cell, all of which are not shown in the figure. This kind of method for growing a single-crystalline thin film is disclosed in, for example, H. Okuyama et al. Journal of Crystal Growth Vol. 117, pp. 139-143 and S. Ito et al. Japanese Journal of Applied Physics Vol. 32, pp. L1530-L1532, 1993.
In growing a ZnSSe single-crystalline thin film by the MBE method, three independent effusion cells are each first filled with one of the three materials, elemental Zn, Se and polycrystalline ZnS and then three kinds of molecular beams simultaneously irradiates upon the substrate from the effusion cells. This kind of method for growing a single-crystalline thin film is disclosed in, for example, W. Xie et al. Applied Physics Letters Vol. 60, pp. 1999-2001, 1992.
In growing a ZnCdSe single-crystalline thin film to form a quantum well by the MBE method, three independent effusion cells are each filled with one of the three elemental Zn, Se and Cd and then three kinds of molecular beams simultaneously irradiates upon the substrate from the effusion cells. This kind of method for growing a single-crystalline thin film is disclosed in, for example, W. Xie et al. Applied Physics Letters Vol. 60, pp. 463-465, 1992.
The MBE method in the conventional art uses many effusion cells in a crystal-growth process. This is because, in order to obtain a single-crystalline thin film having excellent crystallinity, the molecular beam intensities of the component elements of the thin film need to be controlled independently from the others in order that an appropriate intensity ratio can be determined. Since the ratio of the molecule of a molecular beam attaching to the substrate and hence contributing to crystal growth varies depending on the component element, each molecular beam intensity needs to be adjusted. For example, in obtaining a GaAs single-crystalline thin film, the preferable intensity ratio of the As molecular beam to the Ga molecular beam (V/III ratio) is considered to be approximately between 10 and 20.
A problem with the MBE method in the prior art is that the alloy composition and the carrier density vary on the surface of the thin film and/or in the direction of its depth. They also vary according to the process of growing a thin film. Therefore, it is difficult to obtain, with good reproducibility, a single-crystalline thin film having uniform composition and carrier density. This problem has been an obstacle to producing, at a low cost, a device including a ZnMgSSe single-crystalline thin film, ZnSSe single-crystalline thin film or ZnCdSe single-crystalline thin film.
The present invention has been carried out to solve the above problem with the goal of providing a crystal-growing method for forming, with good reproducibility, a single-crystalline thin film having uniform composition and carrier density and a method for producing a semiconductor device by using the crystal-growth method.